[Test] Fix Runtime/protocol_conformance_collision.swift on 11.3+.

This test checks the OS version to decide how to operate but that check isn't right. Revert to a fake future version.

rdar://77389722

Author: mikeash

test/Runtime/protocol_conformance_collision.swift

@@ -47,7 +47,10 @@ func firstHashValue(_ x: P) -> Int {
 }
 
 let osHasWorkaround: Bool
-if #available(macOS 11.3, iOS 14.5, tvOS 14.5, watchOS 7.4, *) {
+// These are deliberately not the standard 9999, as we don't want to hit the
+// special case where it's always available, and we don't want this check to be
+// rewritten in any find/replace operations.
+if #available(macOS 9998, iOS 9998, tvOS 9998, watchOS 9998, *) {
   osHasWorkaround = true
 } else {
   osHasWorkaround = false